Graduate Thesis Or Dissertation
 

Hormonal, experiential and social influences on the reproductive behavior of the vole, Microtus canicaudus

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  • To quantify the reproductive behavior of male and female gray-tailed voles, Microtus canicaudus, under conditions of natural estrus, sexually experienced pairs were observed in a standardized behavior test for 10 hours. The total duration of sexual interactions averaged 223 minutes, which is considerably longer than previously published reports on microtines. The average mount latency, the time from pairing to first mount, also was found to be longer than previously reported. Receptive females rarely showed proceptive (soliciting) or aggressive behaviors; in contrast, unreceptive females were very aggressive. A majority (67%) of male M. canicaudus reached sexual satiety (exhaustion) within a series rather than between series, which is a novel finding for this species. The effect of prior sexual experience on the reproductive behavior of M. canicaudus also was examined. Inexperienced male voles exhibited a significantly longer ejaculatory latency on the first behavioral series than experienced males. In contrast to findings with other rodent species, the effect of sexual experience on qualitative and quantitative measures of male vole sexual behavior was small and transient. The minor differences between experienced and inexperienced males during the first sexual encounter disappeared quickly, with sexual behavior in series after the first being similar for experienced voles. The sexual behavior shown by receptive female voles was similar for experienced and inexperienced females; however the percent females that were receptive was higher in the experimental animals. To investigate the effect of familiarity on behavioral responses of females, voles in post-partum estrus were paired with familiar or unfamiliar males. Sexual behaviors were indistinguishable for females that were paired with the two types of males, supporting the hypothesis indicating that M. canicaudus do not pair-bond. To investigate whether luteinizing hormone-releasing hormone (LHRH) influences the sexual behavior of male M. canicaudus, subcutaneous injections of LHRH (500 ng) were given to intact males and to castrated males with different levels of testosterone replacement. Intact voles, as well as castrated voles with Silastic capsules of testosterone propionate, showed significant facilitation of several parameters of masculine sexual behavior 2 hours after LHRH injection, compared to saline controls. Castrated voles without testosterone replacement showed no sexual behavior, even when injected with LHRH. The observation that in M. canicaudus LHRH can enhance masculine behavior supports the hypothesis that LHRH regulates sexual behavior in this species, as has been suggested for other mammals. The findings also support the hypothesis that the behavioral response to LHRH is mediated by testosterone. The specific behavioral parameters affected suggest that LHRH changes the arousal component of masculine behavior in voles.
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